I have it on all of my systems (4 PCs, 1 laptop), no issues I've noticed yet. The only non-issue was that the install failed the first time it tried on one system, but worked the next time. No idea what happened the first time.

If you have been installing the updates along the way there actually will not be a whole lot of changes except to incorporate them a bit better.
SETI@home classic workunits 4,019
SETI@home classic CPU time 34,348 hours

Same here. I've been running it since day 1 without a single problem. I've always been as up to date with any security or functionality patches as possible. I remember only one update that caused problems a year or two ago, but it caused problems for everybody, and Microsoft had to issue another update to fix the first update.

As a side note, I write software that is deployed to an inertial sensor manufacturing department, and I often have to release it untested. I have production give me any feedback, and I correct any issues within minutes.

The original release of Windows NT 4.0 Service Pack 6 had a major bug in it that could cause data loss during installation. Microsoft had to quickly withdraw the Service Pack until it was fixed and re-released as Service Pack 6a.

Running WIN 7 64bit with Service Pack 1, on my i7-2600 rig, no problems.
Besides my LT, the i7 (2x EAH5870s), is my daily driver. So it'll be used for
video and audio streaming, editting, sometimes a game, but then i'll
shut BOINC down.
(Isn't it on the WINDOWS 7 install disk?) It is in my Dutch version.
So, I ran it from the start, on this host.
Only have to figure out, why BOINC 6.12.26; 64BIT, refuses to finish
install, so nothing, actually, happens(!?)